Variable inductance device



`Fune 10, 1958 J. J. ANTALEK ET AL VARIABLE INDUCTANCE DEVICE Filed Julye, 1955 N TAL 5A V/ m) VIE/@Toes JOHN am! 05527- .Y Y

Arrow/EY;

verneem tNDUCTANCE DEVICE Application July 6, 1955, Serial No. 520,332

8 Claims. (Cl. 336-136) The present invention relates to variableinductance devices, and more particularly to variable inductance devicesof the type having one or more conductive coils mounted on a tubularform in the bore of which a threaded core member is adjus'tablypositioned by rotation of the core relative to the form.

lviany different variable inductance devices of the above mentioned typeare available commercially, some of which include a coil form having apre-tapped or pre-formed threaded bore for the accommodation of thethreaded core and others of which include a coil form in which threadsare cut by the threaded core as it is rotated while initially beinginserted into the form. Both of these prior art arrangements leave muchto be desired when the fabrication thereof by automatic assemblyapparatus is attempted. For example, in both instances it is necessaryto rotate the core member as it is initially inserted into the coilform, thus requiring rather complex apparatus for accurately positioningthe core with respect to the coil which is wound on the outside of theform. Furthermore, relatively small variations in the dimensions of thecore and of the coil form result in wide variations in the torquerequired to adjust the position of the core in the form. Therefore, inorder to maintain this torque within permissible limits when theinductance devices are manufactured on a quantity basis, the dimensionsof the core and of the form must be held within close tolerances,thereby causing the manufacturing cost of such devices to be relativelyhigh.

it is an object of the present invention to provide a new and improvedvariable inductance device.

Another object of the invention is to provide a new and improvedvariable inductance device of the above mentioned type wherein the coreis assembled with the coil form merely by pressing it into the form.

Still another object of the present invention is to provide a new andimproved variable inductance device which may be manufactured on a massproduction basis and in which the torque required to reposition the corein each of the devices is approximately the same even though thedimensions of the various elements of the inductance devices are notheld within close tolerances.

A further object of the invention is to provide a new and improved coilform which facilitates fabrication of variable induetance devices.

A still further object of the invention is to provide a new and improvedvariable inductance device which is reliable in operation, simple indesign, and inexpensive to manufacture.

Briefly, the above objects are realized in accordance with the presentinvention by providing a tubular coil form, on the wall of the bore ofwhich is provided a plurality of spaced, inwardly extending longitudinalribs, the ribs being relatively thin and made of a deformable materialhaving relatively good elasticity. When, therefore, a threaded corehaving a major diameter which is greater than. that of the cylinderdefined by the inside edges of the ribs but less than the insidediameter of the States Patent O coil form proper is inserted therein,the ribs undergo deformation so as to permit the core to be placed atthe desired position in the form, no relative rotation of the core andform being necessary during the assembly operation. As the ribs returnto their normal positions because of the natural elasticity thereof theypress against the threads on the core, and a thread, conforming to thatof the core, is molded in the ribs so as to secure the core in a fixedposition within the form while enabling adjustable movement thereof inthe usual manner by rotation of the core relative to the form.

The invention, both as to its organization and method of operation,together with further objects and advantages thereof, will best beunderstood by reference to the following detailed description taken inconnection with the accompanying drawing in which:

Fig. l is a front elevation view of a variable induc tance deviceembodying the present invention;

Fig, 2 is a longitudinal sectional view of the device;

Fig. 3 is an enlarged section of Fig. 2 taken along the line 3 3thereof;

Fig. 4 is a fragmentary sectional view of the upper portion of thedevice of Fig. l as the core member is being inserted into the form;

Fig. 5 is an enlarged fragmentary sectional view of a portion of thedevice as the core is being inserted into the coil form; and

Fig. 6 is an enlarged fragmentary view of a portion of the device asshown in Fig. 3.

Referring now to the drawing, and more particularly to Fig. l thereof,there is shown a variable inductance device 16 consisting of a tubularcoil form 11 having an enlarged lower portion 12 on which is mounted aplurality of conductive terminal and mounting members 135. The coil forml1 is molded of an insulating material, and in the particular deviceshown, a pair of helical coils 15 and 16, which may conveniently beformed of insulated copper wire, are wound on the coil form 11 and havethe ends thereof conductively connected to different pairs of theterminal members 13. At their lower ends, the terminal and mountingmembers 13 are each provided with a reverse band to facilitateattachment of the device 10 to a chassis. it will be understood thatalthough the inductance device shown in Fig. l to illustrate theinvention is a transformer utilizing a pair of coils 15 and 16, agreater or lesser number of coils may be provided on the form 11, ifdesired.

ln order to adjust the magnetic coupling between the coils 15 and 16 aswell as to change the inductance of each of these coils, a cylindricallyshaped ferromagnetic core member 18 is provided which is arranged withinthe bore 11a of the tube 11 so as to intercept at least a portion of themagnetic field which surrounds the coils le' and 16 when currenttraverses these coils. As best shown in Fig. 2, the core member 18 isprovided with a helical male thread 19 on the outer surface thereof andwith a hexagonal, longitudinally directed aperture 20 for accommodatingthe hexagonal head of a wrench used to rotate the core 18 relative tothe form 1l.

ln accordance with the present invention, a plurality of thin ribs 21are provided on the internal wall 11a of the tubular coil form 11 andextend longitudinally from the top of the form 11 to the vicinity of theenlarged portion 12. r[The ribs 21 are formed integral with the form 11and the roots are relatively thin as compared with the inwardly directedlength thereof. Since the ribs 21 are made of a plastic material whichis relatively deformable, and since the outside diameter of the threads19 on the core 1S is greater than the diameter of the cylinder definedby the inside edges of the ribs 21, but less than the internal diameterof the tubular form 11, the ribs 2l are deformed, being bent over asshown in Fig. 5, so as to permit the core 18 to be accurately locatedaxially within the bore 11a, as the core 18 is inserted into the bore11a either from the bottom or top thereof and is pressed into thatportion of the form 11 in which the ribs 21 are located. Once therelative longitudinal movement between the core 18 and the form 11 isterminated, the ribs 21, because of the elasticity thereof, immediatelybegin to return to their normal positions and as this occurs a thread ismolded into the ribs by the threads on the core member 18. Although theribs 21 are not sufficiently long to engage the core at the innerdiameter of the threads 19, they do not return to their originalpositions wherein they extended inwardly along different radii of theform 11, but remain partially bent over transversely to their respectiveradii as best shown in Figs. 3 and 6. When the ribs 21 occupy thesefinal somewhat deformed positions, however, there is suiiicientfrictional engagement between the ribs and the core 18 to insure thatunder normal conditions the core 18 will not move around loosely withinthe form 11. It will be understood, therefore, that once the core isproperly positioned within the form 11 with respect to the coils 1S and16, it cannot move of its own volition when the device 10 is subjectedto vibration or sudden shocks. Furthermore, normal variations in thediameter of the bore 11a or of the outside dimension of the threads 19,which obtain when normal shop tolerances are permitted in themanufacture of these components, are insufficient greatly to affect thetorque required to rotate the core 1S within the form 11 for adjustmentof the degree of coupling between the coils 15 and 16 or the inductanceof one or both of the coils` Another important advantage achieved by thedescribed structure is that as soon as axial movement of the core 18 inthe form 11 is terminated during assembly of the device 10, the ribs 21begin returning toward their normal position so that further axialmovement between the core 18 and the form 11 is prevented unless theseparts are relatively rotated.

It has been found desirable to employ threads 19 on the core member1S'which are relatively sharp at the outer portion thereof and which arespaced relatively far apart as best shown in Figs. 2 and 4 thereby tominimize the torque required to move the core 18 in the form 11 foradjustment of the inductance or the coupling between the coils, as thecase may be, of the inductance device 1G.

Although many materials having the required characteristics ofdeformability and elasticity may be employed in the construction of thecoil form 11, it has been found that nylon which will withstand the hightemperatures encountered in the applications for which the inductancedevice of the present invention is most suitable and which has suicientstrength and hardness to prevent the ribs 21 from peeling off as thecrore 1S is inserted into the tubular form 11 is most satisfactory.

As best shown in Figs. 3 and 6, when the ribs 21 take their final setpostion in engagement with the threads 19 they are in a somewhatbent-over position. Furthermore, even though the dimensions of thethreads 19 may vary throughout a wide rangefrom one core to another, thearea of those portions'of the ribs 21 which engage the threads 1% remainsubstantially constant due to the fact that the bend obtained inthe'ribs 21 in their iinal set position is dependent upon the relativedimensions of the threads 19V and the inner diameter of the form 11. Forexample, as the outer diameter of the threads approaches the value ofthe inner diameter of the form 11, the permanentV bendV in the ribs 21increases.Y It will be apparent, therefore, that the torque required torelatively rotate the core 13' and the form 11 also remainssubstantially constant irrespective of wide variations in the l. D.ofthe form`11 and the O. D. of the threads 19.

It has been found that when six internal ribs 21 spaced at 60 degreeintervals areV provided inV a coil form 11 and the following dimensionsare held within Vthe tolerances indicated, the torque required to rotatethe cores 18 in the forms 11 varies within a range of from 2 inch-ouncesto 6 inch-ounces. As will be appreciated by those skilled in the art,these tolerances are easily met and the range of torque is particularlylimited, thus preventing, under normal'conditions, undesired spuriousmovement of the core 18 while permitting easy adjustment of the degreeof coil coupling and inductance of the device 1t):

Form material 11. Nylon 10001. Diameter of the bore 11a a .2551.0015inch. Width of the ribs 21 .004i-0005 inch. Radial length of the ribs 21.0088i-00l inch.

As will be evident from the above description, in assembling the cores18 in the tubular coil forms 11 all that is required is to position thecores opposite the bores of the coil forms and then push the cores,without rotation, into the coil forms. These assembly steps may berapidly and easily performed through the use of automatic assemblyapparatus of relatively simple construction.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein which are within the truespirit and scope of the invention as defined in the appended claims.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A variable inductance device comprising a tubular coil form made ofinsulating material, a plurality of thin, circumferentially deflectableribs provided at spaced intervals on the internal wall of said form andextending longitudinally a substantial distance therealong, a coremember having an outwardly threaded portion disposed within said tubularcoil form, the outside diameter of said threads being less than theinternal diameter of said form and greater than the diameter of acylinder defined by the inner ends of said ribs, and at least one coilsupported by said form.

2. A variable inductance device, comprising, a tubular coil form atleast partially constructed ofV an insulating material, a coil mountedon said form, a plurality of circumferentially deiiectable longitudinalribs extending inwardly from spaced positions on the inner wall of coilform, and a ferromagnetic core member disposed within said coil form andhaving a threaded portion which is threadedly engaged by the ends ofsaid ribs, whereby said core member is adjustably positioned withrespect to said coil.

3. A variable induetance assembly comprising a tubular coil form, a coilof conductive material provided on the outer wall of said form, a coreof magnetic material having a threaded portion on the outer wallthereof, the outerdiameter of said threaded portion being less than theinternal diameter of said coil form, said core being disposed withinsaid coil form in close proximity to said coil, and a plurality offlexible and circumferentially deflectable ribs protruding from theinner wall of said form '13 and extending along said tubular coii formlongitudinally thereof, the inwardly extending dimension of each of saidribs being such that said ribs extend at least partially into thethreads of said core.

4. A coil form for a variable inductance assembly,

n comprising, a molded tubular member formed of a exible material andadapted to have a coil wound on the `outer surface thereof, said tubularmember having a plurality of integral, longitudinal ribs which extendinwardly along respective radii from the inner wall of said i tubularmember, the root thickness of said ribs being substantially less thanthe radial length thereof and said radial' length being very small ascompared with the inner diameter of said form, and a ferromagnetic coredisposed within said form, said core being externally threaded forcooperation with said ribs to hold said core in a fixed position withinsaid form, the inwardly extending dimension of each of said ribs beingsuch that said ribs extend at least partially into the threads on saidcore.

5. A coil form for a variable inductance assembly,

comprising, a molded tubular member formed of a nylon and adapted tohave at least one conductive coil wound on the outer surface thereof,said tubular member having a plurality of integral and longitudinallyextending rectangularly shaped ribs on the inner wall thereof, said ribsprotruding inwardly of said tube along spaced radii thereof, the rootthickness of said ribs being substantially less than the radial lengththereof and said radial length being appreciably less than the innerdiameter of said form, and a ferromagnetic core disposed within saidform, said core being externally threaded for cooperation with said ribsto hold said core in a ixed position within said form, the inwardlyextending dimension of each of said ribs being such that said ribsextend at least partially into the threads of said core. 6. A variableinductance device of the type including a threaded core member,comprising, a tubular supporting element constructed of a plasticinsulating material, said element having a plurality of thincircumferentially spaced and integrally formed ribs on the internalsurface thereof which extend along said tubular supporting elementlongitudinally thereof, each of said ribs being deflectable about anaxis passing longitudinally along the length of the rib so that saidthreaded core member may be inserted into said element by means of anaxial force applied to said core member, the outer ends of said ribsextending into interlocking engagement with said threaded core member.

7. A coil form for use in a variable inductance device of the typedescribed in which a threaded core is movably mounted in the form,comprising, an insulating structure formed of nylon and having a boretherein for the reception of said core, and a plurality of spacedyieldable ribs extending longitudinally along said bore and projectingradially therein for interlocking engagement with the threads on saidcore, said ribs having a width no greater than thirty-six one-hundredthsof the radial length thereof and said ribs defining an opening having adiameter less than the external diameter of said core.

8. An assembly for use with a variable inductance device comprising acore supporting member at least partially formed of insulating materialand defining an axially extending opening; a plurality of peripherallyspaced and circumferentially deectable elements on said supportingmember extending at least partially along the axial length thereof andprojecting into said opening; and a core member having a threadedportion, said core member being inserted into said opening tocircumferentially deflect said elements to permit translatory axialpassage of said core member through the opening in said supportingmember to a desired position, said deected elements moving intointerlocking engagement with said threaded portion when said core memberis disposed in said desired position to permit subsequent axial movementof said core member by rotation of said core member.

References Cited in the le of this patent UNITED STATES PATENTS2,462,822 Wood Feb. 22, 1949 2,581,165 Bonanno Jan. 1, 1952 2,631,192Wallin Mar. 10, 1953

